CA2164448A1

CA2164448A1 - Oxidation of organic halogen compounds in wastewaters

Info

Publication number: CA2164448A1
Application number: CA 2164448
Authority: CA
Inventors: Karl Gerhard Baur; Thomas Papkalla
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1994-12-07
Filing date: 1995-12-05
Publication date: 1996-06-08
Also published as: JPH08215689A; CN1131128A; DE4443528A1; EP0716046A1

Abstract

Wastewaters containing organic halogen compounds are oxidized by reacting the wastewaters with nitric acid at from 100 to 350°C under from 5 to 190 bar.

Description

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I
The Oxidation of Organic Halogen Cr , - ' in Wastewaters The present invention relates to a process for oxidizing v~t~vva.~ containing organic halogen compounds at elevated ~ la~ucS and under elevated pressures withrlitric acid.
The removal of organically bound halogen from vva~ represents a problem, especially when the organic halogen compounds are readily soluble in water.
These cnmro.m~ are very often removed from the water by adsorption onto active carbon before the wastewater is subjected to a biological treatment. In this case, disposal of the resulting active carbon is likewise a problem because inainrr~tinn thereof must be carried out in such a way that no dioxin compounds can form, or a safe landfill is necessary for the active carbon. These types of disposal of the active carbon are very costly.
It is an object of the present invention to remedy the above-mentioned a~lvall~.
We have found that this object is achieved by a novel and improved procesi for oxidizing ~va~t~vva~ containing organic halogen ~nmr~lmfie which comprises reacting the ~va.~t~vv..",l~ with nitric acid at from 100 to 350 C under from S to 190 bar.
The present process cam be carried out in the following way:
It is possible to add the amount of nitric acid necessary for breaking down organic halogen cnmro~n~le in particular adsorbable organic halogen compounds (AOX), of from I to 30% by weight, preferably from I to 20% by weight, p,~ .ulally preferably from I to 10% by weight, to the wastewater to be treated in pressurized containers at from l00 to 350 C, particularly preferably from 250 to 300 C, under from 5 to 190 bar, preferably from 30 to 150 bar, ~a ~h,ulally preferably from 70 to 130 bar.
The nitric acid which can be used is ~....,. ~.,~,. '..1 preferably from l0 to 70/0 by weight aqueous nitric acid, IJa~ ,ulally preferably from 30 to 70% by weight technical aqueous nitric acid.
The nitric acid may also already be present, owing to the synthesis, in sufficient amounts in the wastewater and thus need not be metered in. It is also possible to use impure waste acid.
Examples of suitable pressurized containers are tubular reactors or autoclaves .

connected in a cascade.
In a preferred ~lubvdil~ lL, the wastewater is conveyed by a pump through a heat exchanger in which it is preheated to 220 C. SulJa~ u~ ly, the preheated vva~t~ is heated, by directly feeding in 100 bar of stearn or by indirect heating, to 250-C. After the nitric acid has been adjusted to the c.-n~ rnt-~ti.-n necessary for AOX
breakdown in the wastewater at 250 C, the latter is conveyed through a reactor without back-rnixing (eg. tubular reactor which has fittings and is lined with tantalurn or zirconium). After a holdup time of 5 to 30 min, the reaction solution is subjected to uuuut~ ,ull~llL cooling with the feed, and is d~,vlllu~ v.
For the continuous rmh~' ' of the process, it is possible and preferred to use tubular reactors in which the flow of the liquid is adjusted so that there is no back-mixing.
Examples Example I
A wastewater which, besides other impurities, contained p~ lu~lllu~v~ul~onic acid and vil~;LIuulllùlu acid and had a nitric acid content of 16 g/l was subjected to oxidative treatment in a continuous system under the following conditions:
reaction L~ ,IaLul~ = 250~C, pressure = 75 bar, holdup time = 15 min Analytical results for the oxidative treat~nent Sample TOC AOX COD NCS DNCS
[ppm] [ppm] [ppm] [ppm] [ppm]
Feed 1690 6~0 1720 140 2400 Discharge 86 0.5 260 < I 12 Breakdown [%] 94.9 > 99 84.8 > 99 99.5 . .

AOX = adsorbable organic halogen compounds, COD = chemical oxygen demand, NCS = p-nitrochlorosulfonic acid, DNCS = 2,4-dinitrochloro acid Example 2 A ~a~ which, besides other impurities, contained 1-amino-2-cbloro-4-1,ydlu~~ 1"~ nl~n~ was subjected to oxidative treatment in a continuous system with 5% by weight HNO3 at 250 or 265 C urlder 75 bar with a holdup time of 15 min.
Analytical results for the oxidative treatment Test TOC COD AOX
[ppm] [ppm] [ppm]
I

Feed 7400 19600 640 Discharge 1560 3840 110 Breakdown [%] 78.9 80.4 82.8 Feed 7800 18400 720 Discharge 1170 2270 130 Breakdown [%] 85 87.7 81.9 Test conditions 1: T = 250~C, p = 75 bar, holdup time = 15 min, 5% by weight Test conditions 2: T = 265 C, p = 75 bar, holdup time = 15 min, 5% by weight 2~ 64448 Example 3 A wastewater from production of a color pigment, which, besides other impurities, contained t~ a~lllulupllLllalic acid and tetrachloroph~h~ acid in solution as sodium salts was treated with 5% by weight HN03 in a continuous system at 260 C under 80 bar.
Analytical results for the oxidative treatment Sample TOC TCPA TCAM AOX
[ppm] [ppm] [ppm] [ppm]
Feed 2860 1070 5770 3200 Discharge 270 < 5 < 5 120 Breakdown [%] 90.6 > 99 > 99 96.3 TCPA = t~LIà~,lllulu~ dlic, acid TCAM = tetrachlu,~,~,l,ll,,.l,..";i acid Example 4 A wastewater which was loaded with the volatile llyl~u~bulls chloroform, tetrachlu,ul~ , dichloroethane, trichloroethane and tetrachloroethane was mixed with 5% by weight nitric acid and passed through a coiled tube under the conditions of 265 C and 80 bar with a holdup time of 15 minutes, preventing back-mixing by a suitable flow }ate.

AOX TOC C I
Feed mg/1 2465 615 Discharge mg/1 12 6 2400 Breakdown % 99.9 98.9 The example shows that the volatile aliphatic chlorohydrocarbons are virtually Luall~iL~Li~ly eliminated and chlorine is recovered after the treatment as chloride, within the accuracy of the ~ ,~c~ lL.

Claims

1. A process for oxidizing wastewaters containing organic halogen compounds, which comprises reacting the wastewaters with nitric acid at from 100 to 350°C under from 5 to 190 bar.

2. A process for oxidizing wastewaters containing organic halogen compounds as claimed in claim 1, wherein the organic halogen compounds are dissolved in the wastewaters.

3. A process for oxidizing wastewaters containing organic halogen compounds as claimed in claim 1, wherein the reaction is carried out at from 180 to 320°C.

4. A process for oxidizing wastewaters containing organic halogen compounds as claimed in claim 1, wherein the reaction is carried out under from 30 to 150 bar.

5. A process for oxidizing wastewaters containing organic halogen compounds as claimed in claim 1, wherein the reaction is carried out at from 250 to 300°C.

6. A process for oxidizing wastewaters containing organic halogen compounds as claimed in claim 1, wherein the reaction is carried out under from 70 to 130 bar.

7. A process for oxidizing wastewaters containing organic halogen compounds as claimed in claim 1, wherein the concentration of nitric acid in thewastewater is from 1 to 30% by weight.

8. A process for oxidizing wastewaters containing organic halogen compounds as claimed in claim 1, wherein the oxidation is carried out at a pH 6.

9. A process for oxidizing wastewaters containing organic halogen compounds as claimed in claim 1, wherein the reaction is carried out continuously.

10. A process for oxidizing wastewaters containing organic halogen compounds as claimed in claim 1, wherein the reaction is carried out in a tubular reactor.